| As one of transition-metal carbides, TiC possesses not only many special physical properties, such as high melting point, extreme hardness, and outstanding wear resistance, but also exhibits the electric and heat conductivities, which make it highly attractive in the scientific and technological region. Due to the excellent properties, it is widely used in the particulate-reinforced composites, grain refiner, microelectro-mechanical systems, fusion-reactor walls, biocompatible materials etc. The experimental and theoretical studies on TiC cover the fields of materials science, physics as well as chemistry. In this paper, the structural and electronic properties of bulk, surfaces of TiC and Al/TiC interfaces are investigated by the first-principles total-energy pseudopotential method based on density functional theory, which provide theoretical basis for the grain refinement mechanism of Al-Ti-C master alloys.The bulk of TiC is calculated firstly. The band structure, density of states, partial density of states and distribution of charge are simulated and analyzed to understand the electronic and bonding properties of TiC bulk. Through the analysis we could get a conclusion:the bonding nature in TiC can be classified as a combination of metallic, ionic, and covalent characteristics in which Ti-C covalent bonding is the main part; a certain degree of ionicity can be detected, combined with a smaller amount of metallic bonding, which contributes to the high melting point, hardness and chemical stability.By cleaving a bulk TiC after geometry optimize, we could get the TiC slab. By analyzing the change of crystal structure and charge distribution of (001), (110) and (111) surfaces of TiC after full relaxation, we could find that the crystal structures are within a very small change and surface reconstruction does not occur for all of them; the effects of relaxation are mainly localized within the top several atomic layers, not move into deeper layers; changes of charge density decrease from the top to the inner of TiC slabs; strong Ti-C covalent bonding exist between neighboring Ti and C atoms enhanced by the charge depletion and accumulations in the vacuum and interlayer region between atomic layers. Ti- and C-terminated (111) surfaces are employed in the calculation since TiC(111) surface is polar. Among the four surfaces, the surface energy of Ti-terminated (111) surface is the lowest, which shows that the Ti-terminated (111) surface is thermodynamically more stable than the other three surfaces.In the calculation of Al/TiC interfaces, Al(001)/TiC(001), Al(110)/TiC(110), Ti- and C-terminated Al(111)/TiC(111) interfaces has been constructed with the orientation relationship. Change of crystal structure, interfacial charge distribution, interfacial atomic bonding and thermodynamical stability of the four interfaces has been simulated by relaxation. After full relaxation, the crystal structures are within a very small change and surface reconstruction does not occur on the interfaces; the effects of relaxation are mainly localized within the top several atomic layers, not move into deeper layers; interfacial Ti, C and Al atoms all gradually glide along the vertical direction of interfaces, which is show that Ti-Al and C-Al bonds have formed; by analyzing the interfacial charge redistribution, we could find that a mixed covalent/metallic bond is formed between interfacial Ti and Al atoms, and a polar covalent bond for interfacial C and Al atoms, which is stronger than Ti-Al bond for the amount of charge transfer is more than the former; for the C-terminated Al(111)/TiC(111) interface, the ideal work of adhesion is the largest and the interfacial separation is the smallest among the four interfaces, which is show that the C-terminated Al(111)/TiC(111) is the energically most stable interface; for the Ti-terminated Al(111)/TiC(111) interface, the interface energy is the lowest, which is show that the Ti-terminated Al(111)/TiC(111) interface is thermodynamically more stable than the other three interfaces. |
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